The administration of low doses of HgCl2 three times weekly in susceptible strains of mice induces high titers of IgE, IgG1, and autoantibody to fibrillarin, a nuclear ribonucleoprotein involved in pre- ribosomal RNA processing. The anti-fibrillarin response has also been identified as a marker for human scleroderma. Through the use of intra- H-2 recombinants, it has been found that those mouse strains bearing the I-A(s) haplotype are high responders and that the high responder gene(s) is co-dominant. Moreover, this response appears to be reduced by the presence of I-E. The proposed experiments will define further the interactions necessary for a high-titer anti-fibrillarin response. The grant is divided into four Specific Aims. In Specific Aim 1, an allotype-specific ELISA for the detection of anti-fibrillarin will be developed. This assay will provide an important tool for measuring outcomes in Specific Aims 2 and 3. Specific Aim 2 will test critically whether the I-A(s) protein itself is necessary for the anti-fibrillarin response in HgCl2-treated mice. This will be performed by blocking A- A(s) specifically with high-affinity peptides in F1 crosses between susceptible B6.SJL (H-2(s)) and resistant C57BL/6 (H-2(b)) mice. If self-antigen must be presented in the context of I-A(s), then such blocking should decrease the anti-fibrillarin response to HgCl2. Alternatively, it may be that I-A-(s)-linked genes, such as those involved in antigen processing, are critical, and only by blocking both I-A(s) and I-A(b) can anti-fibrillarin production be decreased. In Specific Aim 3, it will be determined whether the anti-fibrillarin response in cognate and MHC-restricted using radiation chimeras. Furthermore, by examining offspring of F1 crosses between B6.SJL and the heterozygous I-E+ transgenic strain B6-Tg-I-Ea(d), it will be tested directly whether expression of I-E is the cause of down regulation. If so, additional chimera experiments will be performed to determine whether it is the expression of I-E itself on B cells that is the cause of down- regulation. Specific Aim 4 will determine whether any Vbeta genes are preferentially involved in the T-cell response to HgCl2. Successful completion of these experiments will focus further research on the possible mechanisms by which this environmental toxin can alter the immune system. This grant proposal is sponsored by Dr. Edward Wakeland, who has extensive experience working in murine genetics and the role of MHC in autoimmune disease. Drs. Robert Eisenberg and Philip Cohens will serve as collaborators on the project. The principal investigator, Dr. Sobel, has been trained in their laboratories. He has worked on in vivo studies of the cellular interactions leading to autoimmunity in the 1pr and gld murine models of SLE. This current proposal thus represents his first attempt at developing an independent project.